1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device and method of driving the same that can have a pre-charging effect without modifying the structures of the gate drive integrated circuits.
2. Description of the Related Art
Recently, liquid crystal display (LCD) devices are being more widely used in a variety of electronic products because of their features such as lightweight, slimness, low power consumption and so on. According to such a trend, the LCD devices have been used in office automation equipment, audio and video equipment and so on. A liquid crystal display device controls a light transmittance in accordance with a signal applied to a plurality of switching devices arranged in a matrix to display desired pictures on a screen. Thin film transistors (TFT) are mainly employed for the switching devices.
Referring to FIG. 1, an LCD device according to the related art includes a liquid crystal display panel 3 in which data lines DL_1 to DL_m cross gate lines GL_1 to GL_n and a TFT is arranged at each crossing for supplying a pixel voltage to a liquid crystal cell Clc. The LCD device further includes a gate driving circuit 2 for supplying a scanning pulse to the gate lines GL_1 to GL_n, a data driving circuit 1 for supplying pixel voltages to the data lines DL_1 to DL_m ; and a timing controller 4 for controlling the gate driving circuit 2 and the data driving circuit 1.
The TFTs supply pixel voltages to the liquid crystal cells Clc via the data lines DL in response to the scanning pulse from the gate lines GL. To this end, a gate electrode of the TFT is connected to the gate line GL, a source electrode of the TFT is connected to the data line DL, and a drain electrode of the TFT is connected to a pixel electrode of the liquid crystal cell Clc. The liquid crystal cell Clc is driven by a voltage difference between a common voltage Vcom supplied to a common electrode and the pixel voltage supplied to the pixel electrode. In each of the liquid crystal cells Clc, a storage capacitor Cst is formed. The storage capacitor Cst may be formed between the pixel electrode of the liquid crystal cell Clc and a pre-stage gate line or between the pixel electrode of the liquid crystal cell Clc and a common electrode line to maintain the pixel voltage in the liquid crystal cell Clc.
The timing controller 4 controls the data driver 1 and the gate driver 2, and supplies digital video signals synchronized to a clock signal to the data driver 1 from a graphic card. The data driver 1 converts the digital video signals supplied from the timing controller 4 into analog video signals (pixel voltages) and supplies the analog video signals to the data lines DL_1 to DL_m to drive the liquid crystal cells Clc in the liquid crystal panel 3. The gate driver 2 sequentially supplies the scanning pulse to the gate lines GL_1 to GL_n to supply the analog video signals to the liquid crystal cells Clc connected to the selected gate line.
In order to prevent flicker and deterioration of liquid crystal in the liquid crystal cells Clc, an inversion driving method may be employed in which the polarity of the video signal supplied to the liquid crystal cell Clc is switched in a designated period. The examples of the inversion driving method are a frame inversion method, a line inversion method, a column inversion method, a dot inversion method, etc. Among these inversion methods, the dot inversion method is generally used in middle to large-size LCD panels.
FIG. 2 is a schematic view illustrating a dot inversion method in which different polarities of the video signal are supplied to each pixel of the liquid crystal panel 3.
Referring to FIG. 2, one square represents one pixel that includes R, G and B sub-pixels. Each of the R, G and B sub-pixels corresponds to one liquid crystal cell Clc. The symbol “+” represents a video signal having a positive polarity and the symbol “−” represents a video signal having a negative polarity supplied to the pixel. Further, FIG. 2(a) and FIG. 2(b) show that the polarities of the pixels are switched after one frame interval. In the dot inversion method, the polarity of the pixel voltage applied to a given pixel is different from the polarities of the pixel voltages applied to the adjacent pixels and is inverted every frame. For instance, in the first frame, the polarities of the video signals shown in FIG. 2(a) are supplied to the pixels, and then in the second frame, the polarities of the video signals shown in FIG. 2(b) are supplied to the pixels.
However, the LCD device driven by such an inversion driving method consumes a large amount of current and the data integrated circuit of the LCD device generates a large amount of heat. To solve such problems, a driving scheme in which the swing width of the pixel voltages is reduced by pre-charging the liquid crystal cells Clc has been suggested. More particularly, when the TFTs connected to nth horizontal line are turned on to supply the pixel voltages to the pixels of the nth horizontal line, the TFTs connected to (n+2)th horizontal line are also turned on to pre-charge the pixels of the (n+2)th horizontal line. As illustrated in FIG. 2, the polarities of the pixel voltages supplied to the pixels of the nth horizontal line are the same as the polarities of the pixel voltages supplied to the pixels of the (n+2)th horizontal line in the dot inversion driving method.
To simultaneously turn on the TFTs connected to the nth horizontal line and the (n+2)th horizontal line, the nth gate line can be simply connected to the (n+2)th gate line. However, in such a case, the pixel voltages already charged in the pixels of the nth gate line can be negatively affected when the TFTs of the (n+2)th horizontal line are turned on. Accordingly, a variety of driving schemes that include changes in the structure of the gate drive integrated circuit have been suggested, but because of the changes in the gate drive integrated circuit, these driving schemes increase the production cost of the LCD device.